1. Field of the Invention
The present invention relates to a feed bar operating device for a transfer press, and in particular to an operating device which performs an advance and return operation on a feed bar.
2. Description of the Prior Art
When a transfer process is carried out in a press machine, the clamping and unclamping of the workpiece is generally carried out by means of the action of advancing and returning of a pair of feed bars which are provided with a plurality of fingers equally spaced in mutual opposition for holding the workpiece. In addition, an advance and return operation takes place by reciprocal motion in the longitudinal direction of the feed bars. This advance and return operation is usually performed by a combination of a planetary gear unit or link mechanism with a gear mechanism. In conventional devices, when the clamping and unclamping action occurs by the advance and return of the pair of feed bars, the movement of the feed bars in the longitudinal direction does not halt completely, but simply comes to a false stop. Accordingly, improving the feed precision becomes a problem, and, because this construction is complicated, manufacturing costs are high. Furthermore, a cam mechanism is used with the pair of feed bars to provide the clamping/unclamping and advance/return operations. However, in the conventional devices, generally a grooved cam or plate cam is used, so that there are many types of problems which arise. Specifically, when a grooved cam is used, a slight space is produced between the cam face and the cam follower, and in addition a slight space between the cam follower and cam follower shaft becomes a problem. When a plate cam is used, the cam follower is pressed against the cam face by a spring or the like, so that when the cam is rotating at a high speed, the cam follower separates from the cam face, making high speed operation a difficult problem.